Re: Win95 won't forget old IP address

["Michael J. Lewis" <[e-mail]>]

Mark Sirota wrote:
> 
> I've got a Windows 95/Plus client which is booting via DHCP.  If I move
> the machine to another subnet, it requests (via DHCPREQUEST) the IP address
> it had before.
> 
> The daemon refuses (DHCPNAK), since the request is coming from a different
> subnet.  The client REQUESTs again immediately, and again the server NAKs.

What server are you using?  In the tests we've done, Windows 95 will respond
with a DISCOVER to a NAK.  The only time the dual REQUEST then continue with
the same address scenario occurs is if there is no response to the REQUESTs
or an invalid response is received.

> And that's it.  The Win95 client doesn't then request a new address on its
> new subnet or anything.  So I tried to make the Win95 machine forget about
> its old address.
> 
> Questions:
> (1) How can I make the 95 machine automagically request a new address on the
>         new subnet?

It should do this.

> (2) How can I make the 95 machine forget its old IP address?

You should be able to run WINIPCFG and RELEASE the address.  This doesn't remove
the address from memory but Microsoft will issue a DISCOVER packet (with the old
address in the Requested Address option) which will eventually result in the client
getting a new address.  (If the address is not available on the network, the Microsoft
client actually will issue three DISCOVERs and only after the last one will it 
actually accept one of the offers.)

If you really want to blow the address away.......

The address is buried in the registry.  The actual location is 

\HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\DHCP\DhcpInfoxx

where xx is a number like 00, 01 etc.  If you have not released the address, 
there will be two fields that point to the remembered address and one to the 
server that granted the address.  If the address has been released, the 
remembered address is x'10' into the block.  
> 
> Question (1) is vital for laptops that might be carried from subnet to subnet.
> Question (2), if easy, would work for desktop machines that switch subnets.
> 
> Thanks for any help you can provide.
> --
> Mark Sirota, Network Systems Engineer
> University of Pennsylvania, Information Systems and Computing
> [e-mail], 215/573-7214